High power diode lasers have been widely used in industrial, graphics, medical and defense applications. The beam divergence and the relatively low output power of such lasers has, however, limited their usefulness.
The output beam of a diode laser is asymmetric due to the beam having a higher angular divergence in the direction perpendicular to the diode junction of the emitter (i.e., the fast axis of the emitter) than in the direction parallel to the diode junction (i.e., the slow axis of the emitter). As a result of the differences in beam divergence, the cross section of the output beam of a diode laser has an elliptical shape, typically requiring the use of a cylindrical lens or other optics to alter the divergence characteristics and shape the output beam for its intended use. Although beam optics can be used on individual diode lasers, in the past the use of such optics has made it difficult to combine multiple diode laser beams into a single beam of sufficient output power to suit many applications.
One method of combining the output beams from multiple lasers is disclosed in U.S. Pat. No. 4,828,357. As shown, the output from each laser is directed using multiple mirrors in order to form a bundle of parallel beams or to cause the beams to converge into a relatively narrow region. The patent discloses that if greater power is required than can be generated by a single beam bundle, multiple bundles of parallel beams can be combined to form a beam bundle of even greater power. The patent does not specifically disclose the use of laser diodes nor does the patent disclose altering the beam shape of the individual laser beams prior to directing the beams into the beam bundle.
U.S. Pat. No. 6,075,912 discloses an alternate technique for combining the output beams from multiple lasers into a single beam. In the disclosed system the output beam of each laser impinges on a discrete facet of a multi-faceted beam deflector. By properly positioning each laser relative to the facets of the beam deflector, all of the output beams are deflected into an optical fiber. The patent discloses interposing an optical system between each laser source and the corresponding beam deflector facet in order to properly image the output beam onto the deflector facet. The patent also discloses interposing an output optical system between the beam deflector and the optical fiber, the output optical system imaging the deflected output beams as a focused group of beam images into the core of the input face of the optical fiber.
U.S. Pat. No. 4,716,568 discloses a laser array assembly formed from a plurality of linear diode laser array subassemblies stacked one above the other, each of the subassemblies electrically connected to the adjacent subassembly. Each linear diode laser array subassembly is made up of a plurality of individual laser emitters mounted in thermal communication with a conductive plate. Although the patent discloses several ways of stacking the subassemblies in order to form the desired 2-D laser array, the patent does not disclose any optical systems for use in combining the output beams of the individual emitters and/or subassemblies.
U.S. Pat. No. 5,887,096 discloses an optical system that is used to guide the output beams from a rectilinear diode laser array to form a substantially uniform radiation field or pattern. In one disclosed embodiment, the optical system utilizes a plurality of reflectors where each reflector corresponds to an individual diode laser. In a preferred embodiment, the centers of the irradiated surface areas of the individual reflectors are situated in a straight line with the distance between a reflector and the corresponding diode laser exit facet being the same for each diode laser/reflector pair.
U.S. Pat. No. 6,240,116 discloses a diode laser array designed to achieve high beam quality and brightness. In one embodiment, the array includes a pair of diode arrays in which the emitting surface planes of the two arrays are displaced from one another in a direction parallel to the one of the optical axes defined by the arrays. The optical axes of the two arrays are offset from each other in a direction perpendicular to one of the optical axes. Lenses are used to reduce the divergence of the output beams. In at least one embodiment, reflectors are used to reduce or eliminate the dead spaces between adjacent collimated beams.
Although a variety of diode laser arrays and beam combining systems have been designed, what is needed in the art is a versatile diode laser assembly which can be easily tailored to specific application needs. The present invention provides such a diode laser assembly.